The present disclosure relates generally to downhole gamma-ray generators, methods to generate gamma-rays in a downhole environment, and methods to log formation data.
Oil and gas companies often utilize different logging techniques to obtain a record of petrophysical properties of a formation, such as, but not limited to, formation density, formation resistivity, formation anisotropy, dip angle of formation bed, radioactivity of the formation, formation porosity, acoustic properties of the formation, and formation pressure properties as well as other properties of the formation (collectively referred to as “formation properties”). Some conventional logging tools utilize always-on, radioactive chemical sources that generate energetic particles, such as neutrons and gamma-rays that interact with the surrounding formation, and utilize sensors to detect resulting signals indicative of the formation properties of the surrounding formation. For example, one commonly used gamma-ray source utilizes Cesium 137 isotopes, which are unstable and emit gamma-rays having energies around 660 KeV as byproducts of radioactive decay. However, Cesium 137 has a half-life of approximately 30 years, and the radioactive decay of Cesium 137 cannot be manually switched on or off. Further, Cesium 137 as well as other commonly used chemical sources are hazardous materials of high environmental impact.
Certain types of gamma-ray sources utilize electron impact ionization as well as direct field ionization techniques to produce gamma-rays. Common designs of gamma-ray sources that utilize the foregoing techniques also utilize an Ultra High voltage (“UHV”) unit in order to generate gamma-rays having sufficient energy to penetrate the surrounding formation. The UHV unit of such designs is often housed in a housing having an outer diameter of approximately 2 inches and a length of approximately 5 feet. In a downhole environment, the length of the UHV unit significantly increases the size, complexity, and cost of the neutron and gamma-ray sources. Further, it may not be feasible to deploy the UHV in an annulus of a production casing or a wellbore due to the dimensions of the UHV.
The illustrated figures are only exemplary and are not intended to assert or imply any limitation with regard to the environment, architecture, design, or process in which different embodiments may be implemented.